Altered expression of growth factors or growth factor receptors may be involved in regulating retinal pigmented epithelial (RPE) cell proliferation after injury or in mediating trophic interactions with the adjacent photoreceptors. This application explores the hypotheses that PDGFs and FGFs cause autocrine stimulation of RPE, and that FGFs, but not PDGFs promote survival of retinal neurons in RPE cells. There are three specific aims in this application, and each is explored through a series of specific experiments. The first aim is to test the hypothesis that PDGFs play a critical role in growth regulation of the RPE, and are relatively more important than basic FGF (bFGF) in this regard. The second aim is to test the hypothesis that bFGF supports the survival of retinal neurons in RPE, particularly after environmental stress, and that they are more important than the PDGFs in this regard. The third aim is to test the hypothesis that FGF receptor function is required for photoreceptor development and for their survival.